This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Members of the family Iridoviridae infect a diverse array of invertebrate and cold-blooded vertebrate hosts. A rapidly growing interest in iridoviruses is not only due to economic concerns, but also due to their involvement in amphibian population declines and infection of mosquitoes. Singapore Grouper Iridovirus (SGIV), a major pathogen in fish aquaculture, has a linear dsDNA genome containing 140,131 nucleotide bp. The icosahedral capsid of SGIV has a maximum diameter of 170 nm. There are three major structural proteins, namely ORF072 (50.5kD), ORF075 (20kD) and ORF018 (32kD). The virion also occupies a lipid layer beneath the capsid shell. The lipid layer is prominently rich in phosphatidylcholine and phosphatidylinositol. Virion morphogenesis takes place in morphologically distinct areas of the cytoplasm termed viral assembly sites (AS). When visualized by electron microscopy, AS appear as a clear region within the cytoplasm that is devoid of large cellular organelles and is close to the nucleus. A majority of matured viruses accumulate in paracrystalline arrays within the cytoplasm and are released by cell lysis, while very few are released by budding through cellular plasma membrane. To date, the detail of viral structure and assembly process is not clear.